Radio frequency power division network



March 29, 1949. 1 G. H. BROWN ET AL 2,465;843

RADIO FREQUENCY POWER DIVISION NETWORK Filed Aug. 16, 1944 zaza A T TOAIVE Y I radiator sections of Patented Mar. 29, 1949 RADIO FREQUENCY POWER DIVISION NETWORK ton, N. 5., assignors '3 Claims.

This invention relates to radio frequency power division networks of the type required for allocating the output of a transmitter to the various a multi-element directive antenna. Such networks are also used with identical connections for determining the directivity of multi-eleroent antennas used for reception, as well as for other purposes where a predetermined distribution of radio frequency power is required.

The principal object of the present invention is to provide an improved network for the distribution of radio frequency power, capable of eflicient operation over a relatively wide band of frequencies.

Another object is to provide a network of the described type wherein the output power ratios remain constant, independent of frequency.

A further object is to provide a network of the described type including means for cancellation of the reactances unavoidably introduced by certain elements of the network.

These and other objects will become apparent to those skilled in the art upon consideration of the following description with reference to the accompanying drawing, of which Figure 1 is a schematic diagram illustrating a power division network designed in accordance with prior art practice; Figure 2 is a schematic diagram of a power division network in accordance with the present invention; and Figure 3 is a schematic diagram of the equivalent circuit of the system of Figure 2. Similar reference characters indicate similar elements in the drawing.

In the design of directive antenna arrays, it is common practice to employ a series of laterally spaced radiator elements or groups of radiator elements, energized with graduated powers. For example, a common type of array comprises four spaced groups of radiators with each-of the two center groups supplied with four times the power delivered to each of the two-outer groups. Ordinarily, all of the groups are identical, so that each presents thesame impedance.

Figure 1 illustrates a typical prior art arrangement for providing the required power division. Four loads l. 2, 3 and 4, each having an impedance Z, are to be energized from a translation device in such manner that each of the loads I and 2 receives percent and each of the loads 3- and d, percent of the power output of the device 5. Although the loads I, 2, e and 4 are represented in the drawing as resistors, it is to be understood that they may be radiator elements or groups of radiator elements-or in fact any load device.

George H. Brown and'Donald W. Peterson, ?rinceto Radio Corporation of America, a corporation of Delaware Application August 16, 1944, Serial No. 549,670

- quarter wave section,

The translation device 5 is connected through a coaxial transmission line 5 to the junction point "i of a pair of similar transmission lines 8 and 9. The line 8 is connected from point 1 to the junction point it of a pair of lines H and [2, leading respectively to the loads 3 and 4. The length of the line section it is unimportant except that it must be considered determining phase relationships between the currents in the loads 3 and 4 and loads 5 and 2. The line 9 is one-quarter wavelength long, or an odd multiple thereof, and terminates at the junction .3 between two similar quarter wave lines it and H5. The other ends of the lines it and i5 are lso connected together at a junction i6 and to a line H. The line H leads to the junction l8 between two lines i9 and '28, which are connected to the loads l and 2 respectively.

It is assumed that the characteristic impedances of all of the line sections in the system are equal to the impedances Z of the loads "I, 2, 3 t. The lines ii and i2 present an impedance of Z/2 to the line 8 at the point ill. A matching stuh 2i is provided on the line B, and adjusted so that the impedance presented thereby at the point i is Z. Similarly, the lines it and 20 present an impedance 2/2 at the point l8, and a matching stub '22 is provided on the line H which thus presents an impedance Z at the point it.

The two parailel quarter wave lines 14 and I5 act like a single quarter wave line having a characteristic impedance of 2/12, and thus reflect the impedance Z to the point Z/ i at the point it. The line 9, being also a inverts the impedance Z/4 at the point it to present an impedance 42 at the point i. Thus the line 6 looks into an impedance eZ, presented by the line 9 and an impedance Z in parallel therewith, presented by the line 8. One-fifth of the energy transmitted by the line '6 will fiow into the line 9 and four-fifths of the energywill flow into the line ii. The energy transmitted by the line Q will be divided equally between the loads l and 2 so that each receives 10 percent of the input power. Similarly, each of the loads 3 and 4 receives 40 percent of the input power. Mismatch of the line 6 at the point l is corrected by means of a stub 23.

The above-described network provides the required power division at one frequency. However, if the frequency is altered, the line sections 9, M and [5 are no longer one-quarter Wavelength, and the stubs 21., :22 and 23 no longer provide complete suppression of standing waves. .Thus the efficiency of the system as a whole decreases,

i5 as an impedance and the ratios of the powers delivered to the several loads are altered.

In the practice of the present system, the desired power ratios are obtained by connecting the loads 3 and d in parallel with each other to the input, and eiTectively connecting the loads I and 2 in series with each other to the input. With this arrangement, the power ratios are maintained constant regardless of frequency. Certain resonant elements are required to provide the series connection. Other resonant elements are provided to compensate their reactances over a wide band of frequencies to maintain eflicient operation of the system as well as accurate power division.

Referring to Figure 2, the input power is applied to a coaxial line comprising an inner conductor and an outer conductor 26. The inner conductor is connected at a point 27 to the inner conductors of a pair of coaxial lines 28 and 29, which correspond to the lines H and i2 of Figure 1 and are connected to the loads 3 and l respectively. The outer conductors of the lines 28 and 29 are connected to a tubular conductor 30, which extends coaxial]; over the conductor 26, and is connected thereto at a The conductor 26 terminates within the conductor 3!] at a point one-half wavelength from the point 3|.

ductor 26, lower end to the lower end of the conductor 25. The lower quarter wave portion 32 of the inner conductor 25 is of larger diameter than the upper portion. The dimensions of the various elements indicated on the drawing are suitable for loads of 50 ohms impedance, and for operation throughout a frequency range of substantially 390 to '725 megacycles per second.

Referring to Figure 3, the portion of the system line, shortcircuited to function as the series resonant circult B. The conductors 3B and 3! cooperate to function as a quarter wave 24.6 ohm line, shortcircuited to act as the parallel resonant circuit C.

general type described on page 855 (Figure 96D) of Radio Engineers Handbook, by F. E. Terman.

The line balance converter includes an input line comprising inner and outer conductors 33 and 34 connected respectively to the conductors 25 A half wave sleeve 35 extends over the conductor 34 end 36. The inner conductor 33 is connected to inner conductor of the line H,

, current flows across the function as the series resonant circuit D (Figure 3). Similarly the conductor 31 and the sleeve 38 constitute the series circuit E of Figure 2. The inner portion of the sleeve 35, together with the surrounding portion of the sleeve 40, constitutes a quarter wave short-circuited line of relatively high impedance, corresponding to the parallel resonant circuit F of Figure 2. Similarly, the inner portion of the sleeve 38 and the surrounding portion of the sleeve 45 comprise the parallel resonant circuit G. The conductors 33 and 34 constitute a 100 ohm coaxial line.

Current flowing into the line 33, 34 goes through the series impedance 31, 38 (D) to the thence through the load I to the outermost conductor 40, which is at ground potential. Current flowing through the inner conductor 33 causes equal and opposite current to flow through the conductor 34. This series impedance 34, 35 (E) to the line 62, and through the load 2 to the conductor 40. Thus the powers delivered to the loads l and 2 re equal, and their sum is necessarily equal to the power delivered to the line 33, 34.

If the frequency of the input power is varied, so that the resonant lengths specified above are no longer one-half wave, one-quarter wave, etc. as stated, the operation will still be the same since the connections of the loads I and 2 are sections 34, 35 and 31, 38.

Since the loads 3 and 4 are equal in impedance and are connected in parallel, the power applied to them through the line 25, 26 will be equally divided. Variation with frequency of the reactance of the quarter wave section 30, 32 is compensated by complementary variation in the reactance of the half wave section 26, 30. Since the line 25, 26 presents an impedance of 25 ohms, and the line 33, 34 presents an impedance of 100 ohms, one-fifth of the power of input will flow to the loads l and 2 while the remaining fourfifths will flow to the loads 3 and 4.

The resistive component of the impedance presented by the line 33, 34 at its input terminals will not remain 100 ohms but will decrease to approximately ohms at the limits of the frequency band. The branch line 25, 26 is loaded by the quarter wave line 32, 35 and the half wave line 26, 30 to simulate the load placed on the line 33, 34 by the line balance converter. Thus the impedance presented by the line 25, 28 at its input terminals varies with frequency from 25 ohms at resonance to approximately 20 ohms at the limits of the band, remaining at all times exactly one-quarter of that presented by the line 33, 34. This provides accurate power division between the two pairs of loads l, 2 and 3, 4 independent of frequency.

The lines 25, 26 and 33, present an impedance of 24 connected in parallel 20 ohms. In order to crate over a wide band of frequencies without variations in performance such as result from the use of matching stubs.

Thus the invention has been described as an improved power division network, providing efficient operation over a Wide band of frequencies without variation in the ratio of the powers supplied to the several loads. The network includes two branch lines, one having an impedance equal to that of two loads in parallel and the other having an impedance equal to that of two loads in series. The first branch line is directly connected to a band of parallel loads. The second branch line is connected through a conventional line balance convertor to the other pair of loads. The line balance convertor divides the power applied thereto equally between the two loads. Thus the system operates as if two of the loads were connected across the input in series and two of the loads were connected across the input in parallel, providing accurate power division in the ratio 1:4:4z1. The line balance convertor is compensated. for a reactance variation with frequency by means of a pair of short-circuited half wave lines connected across the output circuits. Variation of the resistive component of the line balance convertor is compensated by providing a correspondingly varying network on the first branch line, to maintain accurate power division between the two pairs of loads at all frequencies.

The invention covered herein may be manufactored and used by or for the Government of the United States for any governmental purpose without payment to me or assigns of any royalty thereon.

We claim as our invention:

1. A radio frequency power division network including four output transmission lines, each of said lines having a characteristic impedance of Z ohms, four loads each of impedance Z and each connected to one of said output lines, a pair of input terminals, a line balance convertor including an unbalanced input circuit and two balanced output circuits, two of said output lines being connected respectively to said convertor output circuits. a branch line having a characteristic impedance of 2Z ohms connected between said input terminals and said convertor input circuit, a second branch line having a characteristic impedance of Z/ 2 ohms connected at one end to said input terminals and at the other end to the other two of said output lines in parallel, two half Wave short-circuited lines connected respectively to the output circuits of said line balance convertor to compensate variations with frequency of the reactance thereof, and a quarter-wave short-circuited line and a half wave short-circuited line connected to said second branch line to simulate the variation with frequency of resistance of said compensated line balance convertor.

2. A radio frequency power division network for two pairs of loads for dividing power from a radio frequency source among said loads, comprising a first parallel tuned circuit, said first parallel tuned circuit and each load of one of said pairs being connected in parallel in a first parallel connected circuit, a first series tuned circuit, said first series tuned circuit and said first parallel connected circuit being serially connected in a first series connected circuit, second and third parallel tuned circuits each connected in parallel respectively with one of the other pair of loads in second and third parallel connected circuits respectively, and second and third series tuned circuits, said second and third series tuned circuits and said second and third parallel tuned circuits being serially connected in a second series connected circuit, said first and second series connected circuits being connected in parallel to said source, said tuned circuits being tuned to a central operating frequency of said radio frequency source whereby the ratio of power division between said pairs of loads and between the loads of each pair is compensated with respect to fre quency variations of said source to maintain the ratio of the division of power from the source among the loads substantially independent of such frequency variations.

3. A radio frequency power division network for two pairs of loads for dividing power from a radio frequency source among said loads, comprising a first parallel tuned circuit, said first parallel tuned circuit and each load of one of said pairs being connected in parallel in a first parallel connected circuit, a first series tuned circuit, said first series tuned circuit and said first parallel connected circuit being serially connected in a first series connected circuit, second and third parallel tuned circuits each connected in parallel respectively with one of the other pair of loads in second and third parallel connected circuits respectively, and second and third series tuned circuits, said second and third series tuned circuits and said second and third parallel tuned circuits being serially connected in a second series connected circuit, said first and second series connected circuits being connected in parallel to said source, said tuned circuits being tuned to a central operating frequency of said radio frequency source, said series tuned circuits being short-circuited transmission lines of multiple including unity half wavelength long at said central operating frequency, and said parallel tuned circuits being short-circuited transmission lines of odd multiple including unity quarter wavelengths long at said central operating frequency, and line balance convertors one connecting in circuit each said pair of loads, whereby the ratio of power division between said pairs of loads and between the loads of each pair is compensated with respect to frequency variations of said source to maintain the ratio of the division of power from the source among the loads substantially independent of such frequency variations.

GEORGE H. BROWN. DONALD W. PETERSON.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,874,966 Green Aug. 30, 1932 1,952,411 Bohm et a1 Mar. 27, 1934 2,249,963 Lindenblad July 22, 1941 

